Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Ti3sto on June 13, 2005, 08:47:48 PM
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I'd like to know what type(s) of polymerization are involved in polycarbonate.
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im assuming its an addition polymer, since the only polymerisations i know are addition and condensation.
since it doesnt form water as one of the products ( the carbonate is connected to carbon atoms on the repeating structure, not hydrogen), it cant be a condensation polymer
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Thank you so much :)
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Addition polymerisation involves double bonds reacting to give chain growth, usually initiated by free radicals. Polycarbonate synthesis is NOT addition polymerisation.
The synthesis of polycarbonate is a step-growth polymerisation, from most often bisphenol A and phosgene to make LEXAN™.
The first step in the synthesis of polycarbonate from bisphenol A is treatment of bisphenol A with sodium hydroxide. This deprotonates the hydroxyl groups of the bisphenol A molecule, this deprotonated oxygen reacts with phosgene to form a chloroformate. The chloroformate is then attacked by another deprotonated bisphenol A, eliminating the remaining chloride ion and forming a dimer of bisphenol A with carbonate linkage and two molecules of sodium chloride.
Repetition of this process yields polycarbonates, hence step growth polymerisation.
Addition or chain growth polymerisation needs a monomer and initiator and gives a ploymer chain.
Condensation or step growth polymerisation need two different types of chemical to reacts to give a polymer chain plus small molecules such as, but not always, water.